# Exploring shape diversity and sexual dimorphism in two populations of Nigma conducens through geometric morphometrics

## TL;DR

This study uses geometric morphometrics to explore shape differences in two populations of Nigma conducens spiders and finds subtle variations linked to sexual dimorphism and microhabitat.

## Contribution

The study provides new insights into the morphological adaptations and sexual dimorphism in Nigma conducens through geometric morphometrics.

## Key findings

- MANOVA revealed significant but small shape differences between populations and sexes of N. conducens.
- Sexual dimorphism in prosoma shape was observed, likely due to sexual selection or adaptive divergence.
- Shape variations were independent of size, indicating non-allometric relationships.

## Abstract

Spiders are highly adaptable hunters found in nearly all terrestrial ecosystems and play an important role in biological control by preying on pest insects. Spiders’ body size and shape are vital for their survival, particularly in prey capture, and these morphological features are often utilized in cladistic analyses. This study employed geometric morphometrics to investigate prosoma shape and size variations between two populations of Nigma conducens spiders and between sexes within each population. Principal Component Analysis (PCA) explored shape variation, while Canonical Variate Analysis (CVA) compared shape differences between populations and sexes. Multivariate regression analysis was used to check for allometry.

MANOVA results revealed significant shape variations in spider prosoma between the two populations and between sexes, though the degree of these differences was small. The considerable overlap in individual shapes between populations may indicate a response to microhabitat similarity. Additionally, sexual dimorphism was observed in the prosoma shape of N. conducens, likely due to sexual selection or adaptive divergence related to different microhabitats. Size differences between sexes were insignificant in either population, particularly in the first, suggesting that prosoma size does not contribute to reproductive success. Moreover, the non-allometric relationship indicated that shape variations between the populations were independent of size.

Overall, these findings highlight the complexity of morphological adaptations in N. conducens in response to ecological pressures and sexual selection.

The online version contains supplementary material available at 10.1186/s40850-025-00224-4.